Mediastinum

MEDIASTINUM (from the Latin in medio stans - standing in the middle), the space located between the right and left pleural cavities and bounded laterally by the mediastinal pleura, dorsally by the thoracic vertebral column and the heads of the ribs, ventrally by the sternum, and inferiorly by the diaphragm. Superiorly, the mediastinum has no anatomical boundary (the level of the superior aperture of the thorax is considered as such) and passes directly into the median region of the neck. The mediastinum contains many various organs and tissues: the heart with the great vessels (the aortic arch with the ascending and descending parts, the pulmonary artery, the superior and inferior venae cavae), the esophagus, the thoracic lymphatic duct (ductus thoracicus), lymph glands, the vagus nerves (nn. vagi) and the phrenic nerve (n. phrenicus), the thymus gland, the trachea with the two main bronchi, and the cellular tissue and fascial elements surrounding the vessels and airways. From an anatomical point of view, the mediastinum represents a single space not subdivided into separate sections by fascial leaves or muscle masses; however, for practical considerations, it is subdivided by a frontal plane drawn through the trachea and bronchi into two sections - the anterior and posterior (cavum mediastini ant. et post.). The anterior section (mediastinum ant.) contains the thymus gland (in youth), which is later replaced by adipose and connective tissue, further lymph glands, the trachea with the main bronchi, the heart with the proximal part of the great vessels; through the anterior part of the anterior mediastinum, the phrenic nerves pass on both sides from top to bottom. The posterior mediastinum (mediastinum post.) contains the ascending aorta, the esophagus, both vagus nerves, the thoracic duct, the azygos and hemiazygos veins; between all these formations lie lymph glands and adipose tissue. It is important to note that the various organs located in the mediastinum are under the influence of peculiar physical forces that constantly change under physiological and especially pathological conditions. The elastic forces of air pressure, the lungs, and the thoracic skeleton constantly act on the mediastinal organs and are in constant motion due to respiratory activity. Therefore, the mediastinum should be regarded not only as an anatomical and topographical concept - as a receptacle for the organs lying within it - but also as a complex physiologically functioning complex of organs that are highly diverse in their functions, but which, due to the peculiar physical conditions of their activity as mediastinal organs, have something in common that acquires significance not only for their own function, but also in the sense of remote influences on the entire organism. In view of the constant action of a whole series of complex physical influences on the mediastinum (respiration, etc.), the boundaries of the mediastinum (in the living person) change rhythmically under the influence of respiration, and especially undergo prolonged changes and displacement in diseases of the mediastinum itself and surrounding parts, which include mediastinal tumors, aortic aneurysms and aneurysms of the innominate artery, pathological processes in the lungs and pleura (pneumothorax, hydro- and pyothorax, neoplasms), skeletal deformations (of the spine - kyphosis, lordosis, scoliosis; of the sternum and ribs), and diseases of the diaphragm. Diagnosis of mediastinal diseases. The mediastinum can be the site of localization of various pathological processes (inflammatory processes, tumors, etc.). The deep, concealed position of the mediastinum and mediastinal organs, as well as the layered nature of their relationships under both physiological and pathological conditions (in lesions of these organs), make the diagnosis of mediastinal diseases particularly difficult. In diagnosing mediastinal diseases, certain importance is attached to the patients' indications of changes in shape, swelling, dilation of veins, etc., in the region of the upper thorax, as well as complaints of abnormal sensations in the form of changes in pressure, respiration, cough, shortness of breath, irradiation of pain, etc. Existing circulatory disorders manifest as edema, congestion in visible veins, and the development of collateral circulation between the upper and lower vena cava regions. Particularly characteristic is the appearance of those patients in whom compression of the superior vena cava occurs due to a tumor, aneurysm, etc., and, thanks to this, stagnation of blood and lymph in the face and neck region (bloated, swollen face, cyanosis, diffuse swelling of the neck, distended veins). By palpation, percussion, and auscultation, it is possible to determine the presence of swollen glands in the supra- and subclavian region, the presence of significant dullness in exudates, tumors, and similar formations, with simultaneous phenomena of compression of the lung tissue in the corresponding sections. Of very great and often decisive importance in the diagnosis of mediastinal diseases is examination with X-rays, and as a rule one should not be limited only to a radiograph, but should also perform fluoroscopy (of great importance for the diagnostics of movements originating from the heart and its vessels, lungs, esophagus). Injuries. Injuries to the mediastinum are subdivided into closed (subcutaneous) and open (penetrating). A. Closed injuries (subcutaneous). Isolated injuries of the mediastinum are relatively rare thanks to its well-protected position. However, in any severe injury, especially of the upper half of the trunk, the possibility of mediastinal involvement should be kept in mind. According to some authors, the general effect of certain severe injuries (commotio thoracis, etc.) on the organism is explained by the participation of mediastinal organs and nerves. 1. Concussion of the chest (commotio thoracis). Concussion of the chest is rare and is caused by a severe blow to the chest or a concussion (jumping or falling from a great height onto the chest). More or less significant anatomical changes are not noted. As a result of the trauma, shock-like phenomena develop: loss of consciousness, pallor and cooling of the extremities, a drop in blood pressure, disorders of respiration and cardiac activity. Such shock-like phenomena can be transient, but sometimes end in death. The main phenomenon in chest concussion - the drop in blood pressure - is explained by direct concussion of the heart or the influence of the vagus and sympathetic nerves (irritation of the vagus nerve and paralysis of the sympathetic nerve, according to Meola). In the indicated severe injuries, ruptures of the supporting tissue of the mediastinum can occur, as a result of which it loses its role as a tissue supporting the mediastinal organs in a certain normal position and in certain interrelations. Consequently, a disruption of the function and normal arrangement of the mediastinal organs ensues. The blood and lymph vessels of the supporting tissue of the mediastinum may rupture, leading to the formation of blood infiltrates and hematomas in the mediastinum, which, when large, can compress and displace surrounding tissues and cause disorders. Treatment of chest concussion consists in combating shock (horizontal position, morphine, cardiac remedies, infusion of physiological NaCl solution, autotransfusion, sometimes artificial respiration, etc.). 2. Stagnant hemorrhages (blood stagnation from compression, Perthes). In severe bruises and compressions of the chest, "stagnant hemorrhages" are sometimes observed on the neck and head (especially in the conjunctiva and inside the eyeball). The face is dark blue. These phenomena can pass very quickly, but extensive hemorrhages often remain for a longer time. The origin of stagnant hemorrhages is explained by the fact that due to a sudden increase in pressure during trauma (e.g., during chest compression), a strong reverse shock of blood occurs into the initial part of the superior vena cava with simultaneous reflex or voluntary closure of the vocal cords. Ultimately, the cause of the origin of stagnant hemorrhages lies in the region of the mediastinum. 3. Mediastinal hematomas are formed as a result of the violation of the integrity of the blood vessels of the mediastinum both in closed and open injuries of it. Primary and secondary mediastinal hematomas are distinguished. Primary hematomas are observed, apart from stab and gunshot injuries, in the rupture of vessels due to the direct action of blunt violence or in comminuted subcutaneous fractures due to damage to vessels or even the heart by a bone fragment. The clinical significance of primary hematomas is determined by the size of the damaged vessels and concomitant injuries. Secondary hematomas form more slowly or more rapidly on the basis of primary, often insignificant hemorrhages. The growth of the hematoma in such cases is further conditioned by the fact that an exudate from the surrounding tissues is added to the effusion of blood. Due to the pressure exerted by the hematoma on neighboring tissues, pain, shortness of breath, phenomena of nerve irritation, and organ function disorders may appear. The rapid pressure of the hematoma sometimes exerted on surrounding tissues requires urgent intervention. Particularly dangerous is infection of the secondary hematoma, arising hematogenously or lymphogenously, or from the esophagus and bronchi, which can lead to severe mediastinitis. In view of all this, timely clinical and radiological diagnosis of the hematoma is necessary. For the treatment of the hematoma, puncture is mostly sufficient; in rare cases, opening and drainage are required.

Unemptied hematomas of the mediastinum may lead, through their organization, to the formation of scars and callous adhesions, which, as a result of shrinkage, create obstacles to the function of surrounding organs and can cause severe disorders (e.g., of heart activity in the development of mediastinopericarditis). 4. Emphysema of the mediastinum. The accumulation of air (emphysema) in the mediastinum occurs in injuries of the trachea, bronchi, lungs, and more rarely the esophagus. Mediastinum emphysema frequently accompanies closed (especially valve) pneumothorax if the opening in the pleura is located close to the mediastinal cellular tissue, and it can also arise as a result of the spread of subcutaneous emphysema of the neck to the mediastinum. On the other hand, mediastinal emphysema can spread to the neck, leading to the development of subcutaneous emphysema there. The accumulation of air in the mediastinal cellular tissue is a severe complication, because it rapidly leads to the compression of the heart and blood vessels (especially the mediastinal veins), as a result of which severe clinical phenomena develop—dyspnea, cyanosis, stagnation, especially in the region of the superior vena cava, disorders of cardiac activity, and so forth. For the recognition of mediastinal emphysema, the determination of the presence of air in the jugulum (upon the spread of mediastinal emphysema to the neck), clinical phenomena, and X-ray examination are of significance. Treatment is mostly expectant. Sometimes measures are used to reduce the accumulation of air in the mediastinum—providing an outlet for the air to the exterior (an incision in the region of the jugulum, aspiration of air from the mediastinum through the jugulum). B. Open injuries (penetrating). In penetrating injuries of the mediastinum caused by stabbing, gunshot weapons, etc., it is usually a question of injuries to one or another mediastinal organ with the development of the corresponding clinical picture inherent to the injury of the given organ. Wounds of the mediastinum acquire particular significance here in cases where infection is added (purulent mediastinitis), which frequently decides the fate of the patient. - Foreign bodies. In rare cases, foreign bodies, usually gunshot projectiles (bullets, shell fragments), may be encountered in the mediastinum. - Inflammatory processes—see Mediastinitis. Tumors of the mediastinum. In the anterior and posterior sections of the mediastinum, one encounters both primarily arising tumors here and, most frequently, secondary tumors growing into the mediastinum from the side of neighboring organs (sternum, ribs, esophagus, lungs, etc.). Futterer collected 68 cases of mediastinal tumors in the literature. The symptoms of mediastinal tumors usually begin to manifest themselves only upon the enlargement of the tumor, when phenomena of compression of neighboring organs by the growing tumor set in. The signs of compression produced by a mediastinal tumor on neighboring organs are manifested in disorders of respiration, circulation, and so forth, whereby there are observed tightness in the chest, sharp dyspnea (frequently with cyanosis of the face), which is most often the first and earliest symptom of compression of the mediastinum by a tumor, cough, slowing of the pulse (pressure on the vagus nerves), paralysis of the vocal cords (pressure on the recurrent nerves), swallowing disorders, and so forth. Upon the outgrowth of the tumor to the exterior, a protrusion of the chest wall (sternum, ribs) occurs, which considerably facilitates recognition. The diagnostics of mediastinal tumors, especially in the initial period, is often very difficult and even impossible. One must keep in mind here that besides neoplasms, other processes, such as tuberculous lymphomas, gummas, aortic aneurysms, and so forth, can produce the same clinical picture as true mediastinal tumors. In the diagnostics of mediastinal tumors, X-ray examination plays an extremely important role. The prognosis in mediastinal tumors is most unfavorable both in the sense of the outcome and in the sense of the always agonizing course of the disease. Operative treatment of mediastinal tumors yields very little, despite the fact that the main danger (the formation of a pneumothorax) has been eliminated here since the introduction of the pneumopression method by Sauerbruch and Brauer. Mediastinal tumors are subdivided into benign and malignant. Benign tumors are encountered much more rarely than malignant ones. At the same time, it should be noted that the clinical concept of malignancy here does not always coincide with the anatomo-pathological structure of the tumor, because benign tumors upon their growth can, as a result of compression of surrounding organs (respiratory tracts, vessels, heart, esophagus, nerves), cause clinical phenomena proper to malignant tumors. A. Benign tumors can be cystic and solid. Of the cystic tumors in the mediastinum, one encounters almost exclusively congenital cysts of various origins, predominantly dermoids. Dermoid cysts sometimes appear in the jugular notch or at the edge of the sternum; they can open into the respiratory tracts (the discharge of hair with sputum is a sign of a dermoid cyst that has broken through into a bronchus). Cases of complete excision of dermoids with a favorable outcome are known. According to Morris, out of 57 cases of dermoid cysts, an operation was performed in 20. In very rare cases, primary echinococci of the mediastinum are encountered (see Echinococcus), which also give symptoms proper to mediastinal tumors. Of the benign solid tumors of the mediastinum, retrosternal goiters, fibromas, and lipomas (very rare), fibrous mixed tumors (fibromyomas), as well as chondromas and ganglioneuromas (developing from the thoracic part of the sympathetic nerve) are observed. In addition, teratomas are encountered in the mediastinum—cystic, solid, and mixed (partly cystic, partly solid). Teratomas occupy an intermediate place between benign and malignant tumors. B. Malignant tumors of the mediastinum are encountered much more frequently than benign ones (according to Powell, in 90% of all mediastinal tumors). They belong to sarcomas and carcinomas. Of the sarcomatous tumors in the mediastinum, one encounters first of all malignant tumors and formations developing from the lymphatic glands—lymphosarcomas and lymphogranulomas. Mediastinal lymphosarcomas are distinguished by a fairly rapid growth, reach greater or lesser considerable sizes, and give a clinical picture characterized by phenomena of compression of mediastinal organs. Besides lymphosarcomas, lymphogranulomatous formations as a manifestation of lymphogranulomatosis (Hodgkin's disease) are fairly frequently encountered in the mediastinum. The clinical picture of mediastinal lymphogranulomatosis presents partly a symptom complex of a general character, irrespective of the localization of the process, but mainly clinical phenomena generally characteristic of mediastinal tumors (resp. lymphosarcomas). Close to the mentioned tumors stand the frequently encountered aleukemic and leukemic lymphomas of the mediastinum. Finally, ordinary sarcomas are also encountered in the mediastinum, developing from the supporting tissue of the mediastinum or originating from the bony skeleton of the thoracic cage and secondarily growing into the mediastinum. - Carcinoma of the mediastinum can develop from epithelial elements of the thymus gland or misplaced rudiments of the thyroid gland, as well as from mediastinal organs containing epithelium (bronchi, trachea, esophagus). Mediastinal carcinoma develops predominantly secondarily by the ingrowth of a tumor into the mediastinum from neighboring parts or metastatically. The source of origin of such carcinomas are the lungs, bronchi, and epithelium-containing organs of the neck (first of all the thyroid gland). Operations on the mediastinum. The deep, hidden position of the mediastinum makes it little accessible for operative intervention, which becomes possible only upon the violation of the anatomical boundaries of the mediastinum—the division of surrounding bony parts (sternum, ribs) or by approaching it from the side of the neck, the pleural cavity, and so forth. In large operations on the mediastinum, with the aim of reducing the danger of too severe a trauma for the patient, the operation is performed in several stages, wherein the first act of the operation has diagnostic significance (clarification of the diagnosis—orientation regarding the size, position, and type of the tumor). In the second stage, therapeutic intervention is already performed (removal of the tumor). - Operations on the anterior mediastinum. Indications for operations on the anterior mediastinum, besides special indications (injuries of the heart and large vessels), are predominantly inflammatory processes (mediastinitis) and tumors. In addition, operations on the anterior mediastinum are undertaken not only with the aim of obtaining wide access to the mediastinum, but at the same time with the aim of dividing the bony ring of the thoracic cage, the unyieldingness of which is the cause of dangerous phenomena upon the compression of surrounding tissues by pathological processes developing in the mediastinum (especially tumors). To this it should be added that operations on the anterior mediastinum are also performed for the exposure of inoperable tumors with the aim of their radiation therapy (roentgen- or radiotherapy). In the presence of changes (e.g., pus) in the anterior mediastinum, puncture may be required, which is performed in the 3rd or 4th intercostal space at the very edge of the sternum or after trepanation of the sternum. To obtain access to the anterior mediastinum, one makes use mainly of operations on the sternum, which include: atypical subperiosteal resections of the sternum, subperiosteal resection of the manubrium sterni, osteoplastic resection of the manubrium sterni according to Kocher, extirpation of the manubrium of the sternum, median splitting of the sternum according to Milton, anterior superior longitudinal mediastinotomy according to Sauerbruch (vertical incision from the jugulum to the right 3rd intercostal space, longitudinal and, if necessary, transverse division of the sternum), anterior transversal mediastinotomy according to Friedrich, by means of transverse division of the sternum.

In addition to opening the anterior mediastinum through operations on the sternum, access to the mediastinum can be achieved by means of rib resection at the site of their junction with the sternum (parasternal or lateral mediastinotomy). Such exposure of the mediastinum through the formation of musculocutaneous-bone (costal) flaps with various bases is used mostly to expose the heart for the purpose of suturing its injuries. In doing so, attempts are made to expose the heart without damaging the pleura. However, since extrapleural surgery often cannot be performed in mediastinal tumors, many resort to the transpleural route, where a sufficiently wide rib resection provides better access to the mediastinum than operations on the sternum. With the transpleural method, appropriate equipment is naturally used (the Sauerbruch and Brauer differential intrapleural pressure method) to prevent the development of pneumothorax. For operations on the posterior mediastinum in inflammatory processes of the neck, especially those originating from the esophagus and subsequently spreading to the posterior mediastinum, as well as in processes spreading from the posterior mediastinum to the neck (abscesses, mediastinal emphysema), cervical mediastinotomy (mediastinotomia collaris) is employed. In such cases, an incision is made as in esophagotomy, exposing the esophagus, with the incision extended to the jugulum. In deep-seated abscesses and tumors in the posterior mediastinum, posterior, dorsal mediastinotomy is performed (see Mediastinitis).